Add Gitea Actions workflow for amd64 container build

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitea/workflows/build.yaml

@@ -0,0 +1,30 @@
+name: Build Container Image
+
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Build image for amd64
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          file: ./server/Dockerfile
+          platforms: linux/amd64
+          push: false
+          tags: vultr-api-server:${{ github.sha }}
+          load: true
+
+      - name: Test image
+        run: |
+          docker run --rm vultr-api-server:${{ github.sha }} python -c "from vultr_api import VultrClient; print('OK')"